Hydraulic pump



July 26, 1955 T. E. BEACHAM 2,713,829

HYDRAULIC PUMP Filed Sept. 29, 1947 4 Sheets-Sheet l 17v VE/W'OR mom/s 0 w/mo BE/m/w By Ahi'i H% July 26, 1955 T. E. BEACHAM 2,713,829

HYDRAULIC PUMP Filed Sept. 29, 1947 4 Sheets-Sheet 2 IN VENTOR moms 50mm BE/ICHflM July 26, 1955 BEACHAM 2,713,829

HYDRAULIC PUMP Filed Sept. 29, 1947 4 Sheets-Sheet 3 YAJMJ ica y 1955 T. E. BEACHAM 2,

HYDRAULIC PUMP Filed Sept. 29, 1947 4 Sheets-Sheet 4 45a 49a /.9 H506,

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United States Patent HYDRAULIC PUMP Thomas Edward Beacham, London, England, assignor to The Beacharn Hydraulic Company Limited, London, England Application September 29, 1947, Serial No. 776,716 In Great Britain September 17, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires September 17, 1966 3 Claims. or. 103-473 This invention relates to hydraulic pumps of the swash plate type, in which the piston units make direct contact with the swashplate face.

One object of the invention is the provision of an improved pump of this type in which sliding at the contact points between the piston units and the swashplate will be obviated.

Another object is the provision of an improved pump of the said type in which, by simple means, dynamic balance will be achieved.

Another object is the provision of improvements in the inlet and outlet of the cylinders whereby in a simple manner good priming of the pump will be ensured.

Another object is the provision of a compact and strong design of pump affording a high degree of stability to the rotating parts.

Other objects and advantages will appear herein after.

The invention consists broadly of a hydraulic pump comprising a swashplate mounted on a conic crank so as to be freely rotatable relative thereto, and piston units with their axes parallel to the axis of rotation of said conic crank and biased axially with their ends directly against the face of said swashplate, whereby friction prevents said swashplate rotating with said conic crank, and at the same time said piston units are reciprocated by said swashplate, the arrangement being such that a substantially pure rolling movement is obtained between said swashplate face and said piston ends.

In order that the invention may be ,the more clearly understood certain examples of pumps in accordance therewith will now be described, reference being made to the accompanying drawings, wherein: V

Figure 1 is a somewhat diagrammatic longitudinal sectional view of a pump in accordance with the invention;

Figure 2 is a diagram illustrating, the correlation of the swash plate and each of the pistons of the said p p; a

Figure 3 is a longitudinal sectional view in fuller detail of a pump in accordance with the invention;

Figure 4 is a cross section on line IV--IV-of Figure 3;

Figure 5 is a cross section on line V- V of Figure 3;

Figure 6 is a sectionon line VI-VI of Figure '4; V

Figure 7 is a fragmentary section on line VIIVII of Figure 4; I

Figure 8 is a longitudinal section of a somewhat different form of pump in accordance with theinvention;

Figures 9 and 10 are fragmentary views to a larger scale illustrating alternative forms of piston end for contacting with the swash plate.

Referring first to Figure l the reference 1 designates the driving shaft, the reference 2, the conic crank formed thereon and the reference 3 the swash plate mounted coaxially on said conic crank. The pump pistons 4 are arranged in the usual way with their axes parallel to, and spaced around, the axis of the driving Patented July 26, 1955 shaft 1, and each piston is biased by means of a spring 5 so that one end 6 of each piston makes direct contact with the face of the swash plate 3. The spring 5 is a stiff spring having only a small load at the end of the suction stroke. In the usual way the driving shaft 1 rotates in a fixed bearing and the pistons 4 slide in cylinders in a fixed cylinder head, but neither the cylinders nor the control valves therefor are indicated in Figure 1.

It will be seen that the plane of the face of the swashplate 3 passes through the point of intersection of the axis of the driving shaft 1 and the axis of the conic crank 2. The ends 6 of the pistons 4 which engage with the face of the swash plate 3 are spherical, the centre of the spherical surface being on the piston axis substantially at the centre of its mating surface with the cylinder. The swash plate 3 is freely rotatable on the conic crank 2 and the pistons are freely rotatable in their cylinders.

In order to explain the relative motion between the swash plate 3 and the pistons 4 it is simplest to assume that the driving shaft 1 and conic crank 2 are stationary, and that the cylinder head together with the pistons 4 are rotated about the axis of said driving shaft. Obviously this will leave the relative motion the same as if the driving shaft was rotated and the cylinder head was fixed. Figure 2 has been drawn on the above assumption and indicates in end View, to a larger scale than that of Figure 1, a single piston-end 6 at eight different positions around the axis x of the driving shaft. The top position in this figure is that at the outer dead centre position of the piston and the point 0 represents the point on the swash plate surface intersected by the piston axis when in this position. The contact point between the piston end 6 and the swash plate surface is indicated by the small hatched circle p and is vertically below the axis of the piston at a radius depending on the spherical radius of the piston end. As the piston revolves about the axis x (say clockwise) through its eight positions, the piston axis will move along the chain dotted circle. The friction between the pistons and the swash plate will drag the latter round the axis of the conical crank in unison with the rotation of the cylinder head, and the point 0 (which may be regarded as a mark on the swash plate face) will move in a path shown by the dotted ellipse. The relative position between the piston axis and said point 0 at any position of the piston is the horizontal distance d between the circle and the ellipse.

Now under the conditions assumed, the inclination of the swash plate remains fixed and the contact point p remains vertically beneath the piston axis. Thus the relative movement d between said piston axis and the point 0 is always at right angles to the radius from said piston axis to said contact point. Therefore this relative movement, instead of causing sliding merely rotates the piston in its cylinder through the angle 0:. Thus it follows that the relative movement between the face of the swash plate and the surface of the piston end due to the difference between the circular path of the piston axis and the elliptical path of the point 0 is a slight angular oscillation about the point of contact p the angle of oscillation from the position when at the top of the figure being represented by the angle a. The piston oscillates slightly in its cylinder.

Thisoscillatory movement is the only relative movement between said swash plate face and piston end surface. While this relative oscillation is taking place the contact point p is moving steadily round the spherical end surface of the piston, by a rolling action between The angle through which the figure is designated by the reference y and is approximately equal to the angle (1 through which the piston itself has moved around the axis x. The oscillatory relative movement a is so small compared with the rolling movement y that it is absorbed in the elastic stretch and compression of the material, the action being similar to that which takes place in a ball bearing with curved tracks, and in toto the contact between the swash plate face and the piston end is thus substantially a pure rolling contact without friction and therefore substantially without wear.

In addition to the rotary oscillation of the piston in its cylinder there is a small continuous rotation to compensate for the small difference in length between the contact circumference on the spherical piston head and the corresponding contact line on the flat swash plate surface. To accommodate this a slight relative rotation between piston and spring takes place at the end of each stroke where the spring pressure is weakest.

Referring again to Figure l and returning to the true assumption that the driving shaft 1 rotates and the cylinder head is stationary, it will be understood that the swash plate 3 is moved by the conic crank 2 but is prevented from rotating bodily with it by contact with the pistons. The motion of any particular particle z can be divided into two components, one a rotation in a plane at right angles to the axis of the shaft 1 and the other a reciprocation in a direction parallel to said shaft. Now the sum of the centrifugal forces due to the rotation of all the individual particles composing the swash plate will add up to a resultant centrifugal force C1. The inertia forces due to the reciprocation of the same particles together with the inertia loads due to the springs and to the reciprocation of the pistons will add up to a couple T1. The said resultant centrifugal force C1 and the said resultant couple T1 will both be in the plane of the axes of the shaft 1 and conical crank 2 and hence can both be balanced by the centrifugal force C2 exerted by a single balance weight 7 in rigid relation with the main shaft. The centrifugal force C2 is equal and diametrically opposite to the centrifugal force CI but is displaced from it along the axis of the shaft 1 by a distance such that the two centrifugal forces create a torque equal and opposite to the couple T1.

Referring now to Figures 3 to 7 the pump illustrated in these figures is essentially the same as that diagramn'i'atically illustrated in Figure 1, and equivalent parts are designated by the same reference characters. In connection with the obtaining of dynamic balance, however, Figure 3 differs in one respect from Figure 1. This is because in the design of Figure 3 it is not possible to displace the balance weight a distance suflicient completely to neutralise the couple T1. Therefore two balance weights 7a and 7b are employed. The centrifugal force C3 due to the balance weight 7a is diametrically opposite to, and the centrifugal force C4 due to the balance weight "7b is diametrically coincident with, the centrifugal force C1 due to the swash plate 3 and its associated parts. The force C3 is equal to the sum of the forces C1 and C4- and the three forces C3, C4 and C1 together produce a torque equal and opposite to that of the aforesaid couple T1. it will be readily understood that the displacement of the force C3 from the force C1 is not so great as would be that of a force C2 which was equal to the force C1 and which produced a couple with the force C1 of the same value as that produced by the three forces C3, C4 and C1.

It will be seen that, in the pump illustrated in Figures 3 to 7 there are six pistons, viz. three relatively small diameter pistons 4a and three relatively large diameter pistons 41). These pistons are shown as being at the same radius with respect to the axis of the shaft 1 and being disposed alternately around said axis as shown in Figure 5, but they could obviously be at different radii and differently disposed. The pistons 4a move in cylinders 8a and the pistons 4b in cylinders 8b, all said cylinders being constituted by bore holes in a cylinder head or block 9.

The cylinders all draw liquid from a common inlet 1.0, but the cylinders 8a deliver to a high pressure outlet 11, whereas the cylinders 8b deliver to a low pressure outlet 12. More particularly the inlet 10 leads to liquid space 13 at the rear end of the cylinder block 9 remote from the swash plate 3. All the cylinders take in from this space 13 under control by valves 14a, 14b of the mushroom type. The pistons 4a and 4b, when at the inner end of their stroke come very close to the respective valve heads and the outlet ports 15a and 15b extend radially from the cylinders close to the valve heads. In order to prevent the pistons 4a and 4b closing the outlet ports 15:: and 15b, the cylinders at their ends close to the valve heads are counter-bored eccentrically as at 16a, 16b so that there is always a small clearance to one side of the pistons from which the outlets 15a, 15b extend. As will be seen from Figure 4 the counter-bores are tangential to the main bores on the side opposite to the radial outlet ports 15a, 15b. The valves 14a and 141) may be coaxial with the eccentric portions 16a and 16b of the cylinders.

The outlet ports 15a lead past respective non-return ball valves 17 into spaces 18a within the cylinder block 9. In the case of one of said spaces 18a (the uppermost according to Figure 4) said space communicates direct with the high pressure outlet 11 by way of passages 19 (Figure 6). Also all three of said spaces 18a communicate with each other, by way of conduits 20 in the cylinder block 9 which meet at the centre. In other words all three of said spaces 18a communicate with the high pressure outlet 11.

The outlet ports 15b lead, in like manner, past respective non-return ball valves 17, into spaces 18b in the cylinder block. These spaces 18b communicate, by way of conduits 21 with a centre space 22 in the cylinder block, which centre space is in direct communication with the pressure outlet 12. It will be readily seen that, if all the cylinders were required to discharge to one outlet only, all the spaces 18a, 18b could be made to communicate with the said centre space 22.

It will be seen that when any piston is at its inner dead centre position the total effective cylinder volume consists of the very small clearance beyond the end of the piston plus the small crescent shaped clearance partially surrounding the piston due to the counter bore plus the small space within the outlet conduit up to the ball valve 17. This volume is relatively very small and this ensures a satisfactory lift of the inlet valve 14a or 14b when the piston commences its suction stroke.

Describing now in more detail the construction of the pump, it will be seen that the swash plate and associated parts are housed within a housing formed by a hoodshaped casting 23 bolted to the front of the cylindrical cylinder block 9. The fluid space 13 is constituted by another and flatter hood-shaped casting 24 bolted on the back of said cylinder block 9 and it will be seen that the castings are bolted by common bolts 25.

The driving shaft 1 bears, in ball bearings 26, in the front wall of the casting 23. The combined balance weight 7a, 7b is threaded on and keyed to said driving shaft and is engaged at the rear by a shoulder 27 on said shaft. At the front said combined balance weight engages the inner race 28 of said ball bearings 26, and the outer race 29 engages at the front a shoulder 30 of the front wall of the casting 23. Thus the ball bearings 26 cal crank 2 said swash plate is formed with a forwardly projecting flange 3a near its circumferential periphery and with a rearwardly projecting boss or snout 3b closely surrounding said conical crank. Ball bearings 33 are provided between said flange 3a and the crank 2 and roller bearings 34 are also provided between said boss and said crank. The inner race 35 of the ball bearings 33 abut at the front side against a shoulder 36 on the conical crank, and a shoulder 37 on the swash plate abuts at the front against the outer race 38, and thus said ball bearings 33 take the end thrust on the swash plate.

The bore holes in the cylinder block 9 which form the cylinders 8a and 8b are counter-bored from the front face of said cylinder block, and bushes 39a and 3% are screwed into the counter borings, said bushes having bores which form continuations of the bores in the cylinder block so that the pistons can slide freely in the continuing bores in the bushes and the cylinder block. The bushes 39a and 39b extend forwardly from the front face of the cylinder block so that long bearings are formed for the pistons.

The aforesaid springs 5 embrace the bushes 39a and 39b and are in compression between the front face of the cylinder block and discs 40 mounted on the pistons as will be clear from the drawing.

The seats 41 and the supports or cages 42 for the valves 14a and 14b are made separate. For receiving these valve seats and valve cages, the cylinder block 9 is counterbored and tapped coaxially with, and up to, the eccentric portions 16a and 16b of the cylinders, as will be clear from the drawing. The seats 41 are put in first and the cages 42 are screwed in afterwards, thus retaining the seats as will be clear from the drawing.

The spaces 18a and 18b in the cylinder block to which the outlet ports 15a and 15b lead from the cylinders, are constituted by boring into the circumferential periphery of said cylinder block and plugging the bores by means of screw plugs 43. The springs 44 which bias the ball valves 17 against their seats are housed in recesses in these plugs. In the case of that plug 43 which is illustrated in Figure 6, the outlet conduit 11 extends coaxially some distance into the outer end of this plug and is connected to the space 18a by means of the aforesaid passages 19 which extend through the plug from said conduit 11 around the spring 44 and ball 17.

As shown the pressure outlet 12 is constituted by a tube 45 coaxial with the cylinder block which passes in sealed relation through the wall of the casting 24 and is screwed into a tapped hole in the rear face of the cylinder block, which hole communicates with the centre space 22. Thus said centre space communicates with said outlet 12 as aforestated.

In order to lessen the inertia forces, the larger pistons 4b may be made hollow.

Referring now to Figure 8, this illustrates an embodiment of the invention which dilfers in various ways structurally from that just described. In this figure parts which correspond to parts shown in the preceding figures have been designated by the same references. The respects in which the arrangement of Figure 8 ditfers from that of Figures 3 to 7 are as follows:

The pistons 4 and cylinders 8 together with their eccentric portions 16 are all the same size and all deliver to a common outlet. This outlet is similar to the outlet 11 of Figure 4 and is not seen in Figure 8. The bushes 39 are accordingly also identical with each other.

The swash plate 3 instead of running on one set of ball bearings and one set of roller bearings runs on two sets of ball bearings. Thus the flange 3a extends further axially forward from the swash plate proper. Ball bearings 33, which are similar to the similarly designated ball bearings of Figure 3, and take the end thrust in substantially the same manner, are provided between the crank 2 and the forward portion of said flange, and, between said crank and the rear portion of said flange, smaller ball bearings 46 are provided. The two sets of ball bearings are spacedapart axially far enough to afford a fully stable bearing for the swash plate.

Instead of the projection 31 of Figure 3 which bears in roller bearings 32 an additional set of ball bearings 47 are provided for the driving shaft 1, spaced forwardly of the ball bearings 26. To this end the casting 23 has a further casting 48 bolted to its by means of bolts 49, and both the ball bearings 26 and the ball bearings 47 are provided between the driving shaft 1 and this casting. It will be seen that the ball bearings 26 take the end thrust in the same way as the similarly designated ball bearings of Figure 3.

A minor point of difference between Figure 3 and Figure 8 is that whereas, in the case of Figure 3 the dual balance weight 7a, 7b is located between the shoulder 27 and the inner ball race 28, and the inner ball race 35 bears directly against the shoulder 36, in the case of Figure 8, the single balance weight 7 is located between the inner ball race 35 and the shoulder 36, and the shoulder 27 bears directly against the inner ball race 28.

In any of the preceding figures, instead of the pistons being each provided with a spherical end 6 for engaging with the swash plate face, they may be each provided with an end 6a, whose surface, as shown in Figure 9, is spheroconical, or with an end 6b whose surface is conical.

In the first case the region of contact p of Figure 2 will be slightly elongated in a sense radially of the piston, and in the second case said region of contact will be still further elongated in the same sense. It will be clear to those skilled in the art that this will not affect the explanations given herein with reference to Figure 2.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A hydraulic pump comprising a rotatable conic crank, a swash plate mounted on said conic crank, a cylinder block, cylinders constituted by bore holes bored into said cylinder block parallel to the axis of rotation of said conic crank, pistons in said cylinders, said pistons being arranged to be reciprocated by said swash plate, each cylinder including an inlet port in the end remote from said swash plate and an inlet valve controlling the said inlet port, each cylinder including an outlet port in the side leading to a valve chamber, each valve chamber being constituted by a recess formed in the periphery of said cylinder block, screw plugs each screwed in the mouth of a respective recess, a non-return valve for each valve chamber controlling the flow of liquid from a cylinder to the respective valve chamber, said cylinder block including straight bore holes issuing from each valve chamber, whereby all of said valve chambers are connected to each other within said cylinder plug, each of said screw plugs, except one, forming an impervious closure for its recess, and said one screwplug having a common outlet through it for all of the valve chambers.

2. A hydraulic pump comprising a rotatable conic crank, a swash plate mounted on said conic crank, a plurality of cylinders with their axes parallel to the axis of rotation of said conic crank, pistons for said cylinders, said pistons being arranged to be reciprocated by means of said swash plate, each cylinder including an inlet and an outlet conduit and inlet and outlet valves for controlling said conduits, a plurality of said cylinders being of relatively small diameter and having their outlet conduits in communication with a common low capacity outlet, and another plurality of said cylinders being of relatively large diameter and having their outlet conduits in communication with a common high capacity outlet.

3. A hydraulic pump comprising a rotatable conic crank, a swash plate mounted on said conic crank, a cylindrical block formed with bore holes parallel to the 7 axis of rotation of said conic crank, the said bore holes constituting cylinders, pistons in said cylinders, said pistons being in operative engagement with said swash plate so as to be reciprocated by the same, the bore hole of each cylinder being extended toward the side of the cylindrical block remote from the swash plate, the said extensions having a larger diameter than said bore holes, an annular valve seat member located-in each of said extensions and abutting against a shoulder formed where each extension meets the respective bore hole, a separate valve cage for each of said valve seat members, each cage comprising an outer sleeve portion, a central bush portion and arms joining said sleeve portion to said bush portion, said valve cages being screwed into said extensions thereby retaining the valve seat members in place against the respective shoulders, a plurality of inlet valves of the poppet type each disposed with its head within one of the cylinders and with its stem bearing slidably in the respective bush portion, a plurality of springs each biasing one of said poppet valves to abut 20 its head against the respective valve seat member, each of said cylinders including an outlet port in its side, and a References Cited in the file of this patent UNiTED STATES PATENTS 880,731 Hall ,et al. Mar. 3, 1908 1,427,740 Johnson Aug. 29, 1922 1,714,148 We1d y May 21, 1929 1,820,266 .Bilderbeck Aug. 25, 1931 2,093,477 Parsons Sept. 21, 1937 2,138,194 Pfauser Nov. 29, 1938 2,169,456 Wahlmark Aug. 15, 1939 2,188,035 Dauster Jan. 23, 1940 2,193,612 Alden Mar. 12, 1940 2,248,449 Dudley July 8, 1941 2,261,471 Hull Nov. 4, 1941 2,268,000 Treer Dec. 30, 1941 2,423,373 Chandler July 1, 1947 FOREIGN PATENTS 484,114 Great Britain May 2, 1938 

